1. Field of the Invention
The present invention relates to apparatus and method for direct and rapid forming of a ceramic work piece; more specifically, the present invention provides an apparatus and a method for directly, rapidly, and precisely fabricating a three-dimensional (3-D) ceramic work piece by a high energy beam, skipping the conventional process of sintering a ceramic workpiece in a furnace.
2. Description of Related Art
In the past decades, rapid prototyping combining the latest computer, manufacturing, and material science technology has provided a number of fabricating methods for producing three-dimensional, or 3-D, workpieces directly and rapidly. These fabricating methods vary in that some employ light energy to induce chemical bonding among involved materials, some employ heat fusion, and some employ adhesive to glue fragments of the workpiece together, etc. In terms of material used, metals, ceramics, polymers, and others are all possible candidates. Since different fabricating methods use different forms of energy to produce the desired workpieces, said rapid prototyping technology can be sorted into five different categories based on materials, bonding mechanism, and forms of energy involved during the fabricating process:
1. Stereo Lithography (SL) --U.S. Pat. No. 4,575,330 to Charles Hull, 1986. Dr. Brady of University of Michigan describes a process based on the Stereo Lithography method that uses ceramic resin (a mixture of ceramic powder and light-sensitive resin) as a raw material and exposes such material under a directed ultra violet light in order to solidify said liquid state resin. This process bonds ceramic powder, forms clay-like ceramic green parts, then removes the binder while increasing the density of the ceramic green parts at the same time with prior ceramic sintering technology.
2. Selective Laser Sintering (SLS) --U.S. Pat. No. 4,863,538, September, 1989 to Mr. Deckard of University of Texas at Austin represents this technology, which was invented in 1986, and has been subsequently commercialized by DTM company. The SLS technology can be applied to various materials to produce 3-D RP workpieces as long as the material is in the form of powder. At present, the SLS technology comprises the steps of covering ceramic powder with resin, melting the resin with a laser so that the resin acts as a bonding agent to the ceramic powder for forming a ceramic green part and then processing the ceramic green part with conventional ceramic sintering technology to obtain the final ceramic workpiece. A typical material used in the SLS process is aluminum oxide and some polymer compounds.
3. Fused Deposition Modeling (FDM)--Such technology involves heating a raw material until it melts, then material strands are extruded, which will be further shaped by FDM to form a 3-D object. Professor Agarwala, of Center for Ceramic Research at Rutgers University, has been implementing such FDM technology with ceramic powder and organic binder mixture in making material strands, the ceramic green part formed is then sintered by conventional ceramic sintering methods to obtain the final ceramic workpiece.
4. Three Dimensional Printing (3DP)--The 3DP technology is represented by the Three Dimensional Printing method (U.S. Pat. No. 5,204,055, April 1993, Sachs et al.) of Massachusetts Institute of Technology, which entails technologies similar to the ink jet technology in that binding agent is selectively spurted out and onto a designated powder material. Such process starts by laying a thin layer of powder, spurting liquid binder from the nozzle and onto the surface of the powder layer, wherein the powder layer in the affected area will glue together to form a thin cross section. The above steps are repeated until a three-dimensional object is formed. If the subject raw material is ceramics, then the above steps will form a solid three-dimensional ceramic green part, and conventional ceramic sintering technology will complete said 3DP process in forming a final, sintered ceramic workpiece.
5. Laminated Object Manufacturing (LOM)--U.S. Pat. No. 4,752,353, Feygin, owned by a U.S. company named Hydronetics, describes a technology that utilizes a laser beam to carve out a cross section of a 3-D object on a thin slice of material in its solid state, then glue these thin slices one on top of another in later stages to form a 3-D object. After thin slices of a certain material are formed, adhesive is applied between thin slices with each stacked on top of another. A final 3-D object is then formed as soon as all the slices are bonded together with adhesive. Such a process can be applied on materials including paper and sheet metal. However, in the case of ceramics as the prime composition material, each ceramic thin slice is pre-fabricated with ceramic powder and polymer binder, then the aforementioned LOM process is applied. Each ceramic thin slice is shaped by a directed laser beam into a corresponding cross section layer of a 3-D workpiece. Then when all the thin slices corresponding to the cross sections are shaped, a 3-D ceramic green part can be formed by stacking and gluing all the slices one on top of another. A final ceramic workpiece can be obtained this way after the green part is sintered in a furnace.
The above-mentioned technologies, sorted in five categories, are all related to the forming of ceramic green parts and all require further sintering equipment for final ceramic sintering. Since ceramic green parts fabricated by the conventional rapid prototyping machine need to be further calcined, or sintered, in a furnace to obtain the final ceramic workpiece, these processes are then referred to as indirect ceramic making process. While the above-mentioned indirect process of ceramic making can make workpieces of complex configurations and can save the usage of molds and dies, there are drawbacks such as: requiring further sintering steps, which demands both additional equipment and technical know-how; requiring further removal of the binding agents during the conventional sintering, which prolonges the processing time since the entire ceramic making process can not be completed in consecutive steps. Therefore, it has long been an object of the rapid prototyping machine manufacturers to devise a way of forming ceramic workpieces directly and rapidly by a rapid prototyping machine, skipping the conventional ceramic-sintering phase in a furnace.